WASHINGTON (CNN) --The FBI on Wednesday advised state and local law enforcement agencies that the capture of al Qaeda operations chief Khalid Shaikh Mohammed could spark terrorist attacks already planned.

The FBI, in its weekly intelligence bulletin to police agencies, said it believes the capture of Mohammed deals "a severe long-term blow" to al Qaeda's ability to plan and carry out attacks against the United States. But officials worried about plans that may already be in the pipeline.

"In the short term, the apprehension may accelerate execution of any operational planning already under way, as operatives seek to carry out attacks before the information obtained through Mohammed's capture can be used to undermine operational security," the FBI said.

But an FBI official told CNN that despite the concern expressed in the dispatch, authorities have no information indicating there is any specific or credible threat as a result of the capture.

Mohammed is suspected of masterminding the September 11 attacks.

Interrogators are placing "all appropriate pressure" on Mohammed at an undisclosed location, U.S. officials have said.

Government sources have said Mohammed has not been particularly useful so far, but that he has begun to talk. Initially, the suspected terrorist limited his responses to recitations from the Koran, the Islamic holy book, the sources said.

But human rights group Amnesty International said Wednesday that interrogation techniques used on Mohammed and on other alleged terrorists amount to torture.

"Despite claims to the contrary by U.S. officials, the use of sensory deprivation (hooding), prolonged physical restraint (shackling) and denial of needed medical care are all characteristic elements of torture, and like psychological torture, are prohibited under international law," the group said in a statement. (Full story)

The FBI statement, intended for law enforcement officials, noted several members of Mohammed's family living outside the United States are known to have been affiliated with al Qaeda.

One of Mohammed's nephews, Abd al-Karim, speaks English and is described as being familiar with life in the United States from his years spent studying in North Carolina in the mid-1980s (Full story).

Both Mohammed and al-Karim studied at North Carolina Agricultural and Technical State University in Greensboro. They left the United States in 1986, after Mohammed earned an engineering degree.